Synthetic organic polymeric materials (hereinafter often synthetic polymers) have been known and produced and used commercially for several decades in very large quantifies. One of the most common of such polymers for several years has been poly(ethylene terephthalate), sometimes referred to as 2G-T, which is a polyester and is currently produced in very large quantifies in the form of oriented structures, such as filaments and films and articles thereof and/or therefrom, such as fabrics and garments. It has long been desired to find a way to reduce the flammability of polyester articles, i.e., shaped articles incorporating (generally oriented) structures of polyester, especially garments and other articles of apparel and fabrics, including filled articles, furnishing articles of and filled with polyester fiber, and polyester films, including tapes, by way of example.
The literature is full of various suggestions for solving this problem, all of which have various disadvantages or difficulties, especially practical and economic, so that there still remains this long-standing problem requiring solution. This problem has not been restricted only to polyesters, but has applied to articles of other synthetic polymers. One solution suggested in the 1950's will now be discussed.
A process of multiple-neck drawing while simultaneously infusing various modifying agents in finely divided form into polymeric articles was disclosed some 30 years ago, by Adams in U.S. Pat. Nos. 3,233,019 and 3,102,323, the disclosures of which are hereby incorporated by reference. Although additives that Adams desired to infuse were mostly dyestuffs, he also disclosed other additives and modifiers, including antistatic agents, light stabilizers and cross-linking agents (col. 2, lines 31-32 of U.S. Pat. No. 3,102,323), and incompatible polymers, lubricants (including silicones), flame-proofing agents and flame retardants, inorganic salts, wetting agents and hydrophobic agents, anti-soilant additives, adhesives and bonding agents were also among those listed (cols. 13-14). His first Examples were of 2G-T filaments imbibing dyestuffs, but he mentioned other polymers, including polyamides (nylons) and polyalkylenes, such as polypropylene and polyethylene. By "modifying agent," Adams meant essentially any substance soluble in the "cracking agent" which was not substantially removed subsequently (col 2, lines 39 et seq of U.S. Pat. No. 3,233,019). Adams disclosed definitions of expressions used herein, including "cracking agent", and referred to an earlier article by Woods (J.T.I. Transactions, vol 46, pages 629-631, September, 1955) discussing the phenomenon of surface cracking of nylon yarn, the disclosure of which is also incorporated herein by reference. Adams taught multiple-neck drawing as a prerequisite for infusing his "modifying agents" (col 3, lines 57-59 of U.S. Pat. No. 3,233,019) and referred to his multiple neck process in his claims and elsewhere (e.g., previous col 2, line 29), but the term "multiple-neck drawing process" was earlier used by Woods (see bottom of col 4 of U.S. Pat. No. 3,102,323). We refer herein to Adams' techniques as "imbibition drawing", which term has become accepted by many. The present invention concerns improvements in the imbibition techniques disclosed several decades ago by Adams. So far as known to us, his process is not being used commercially successfully to incorporate flame-retardants to solve the long standing problem of flame-proofing articles of polyester fibers or films, nor used otherwise commercially.
The lack of successful commercial application of Adams' process has persisted until now, notwithstanding the more recent disclosures by Guthrie et al in U.S. Pat. Nos. 4,001,367 and 4,055,702 of a method for permanently incorporating between 0.1 and 25% by weight of an additive into an undrawn or partially drawn melt spun fiber formed from a polyester, polyamide, polypropylene or high density polyethylene by cold drawing the fibers under conditions that generated a network of interconnecting microvoids within the fiber, and formed in the presence of specified liquid or vapor media (i.e., fluids) which filled the microvoid network at temperatures below the effective glass transition temperature (T.sub.g) of the fibers. Guthrie's additives could be virtually any liquid or solid additive that could be dissolved, dispersed or emulsified in a suitable liquid or vapor, and should have a maximum particle size less than two microns. Guthrie's additives could either be present in his drawing medium which filled the microvoid network, or could be applied to a drawn fiber wherein the microvoids contained the drawing medium. In this later alternative, the additive diffused into the microvoids and displaced a portion of the drawing medium. Guthrie's Examples concerned mostly incorporation of phosphorus-containing flame-retardant additives into 2G-T fibers. The flammability of Guthrie's resulting dyed and undyed fabric samples was determined using the Limiting Oxygen Index (LOI). The best (highest) LOI value reported by Guthrie was 28.8 (Example 7, col 15, line 32).
Adams referred to and illustrated the non-uniform axial distribution of modifier in the products of his invention as an unexpected and valuable property (e.g., col 3, lines 23-26 and 35 et seq of U.S. Pat. No. 3,102,323). We believe, however, that the inability of Adams or Guthrie to distribute finely divided modifiers (additives) more uniformly may have been responsible for previous difficulty in "imbibing" relatively large loadings of additive without negatively affecting important properties, such as tensile properties.
More recently, some of the present inventors have published a series of Russian papers on compositions comprising a polymeric matrix and low molecular weight compounds (LMCs) that are incorporated into the matrix via formation of a highly dispersed porous structure of crazes, when polymer drawing takes place in adsorptionally active media (AAM), referred to in the Journal of Thermal Analysis, Vol 38 (1992), 1311-1322, and in Polymer Science, Vol 34, No. 6, 1972, 476-477, each being incorporated herein by reference. We have mostly used herein the terminology "imbibition drawing" and Adams' terminology of "cracking agent", or "cracking fluid" or "cracking liquid". We have also used the term "crazes", which has been used in the art for at least 20 years.
The present invention solves the specific problems referred to above, and provides improvements whereby a wide variety of finely divided additives can be introduced into articles of synthetic polymers, broadly, by process techniques that have many flexible attributes, so are expected to be important and have broad commercial application as will be apparent.